When a hot-dip coated steel sheet is manufactured, first, a steel sheet is conveyed in a hot-dip coating bath, and coating is applied to front and rear surfaces of the sheet. Subsequently, gas such as air is sprayed from a wiping nozzle toward the front and the rear surfaces of the sheet while the coated steel sheet is drawn outside the hot-dip coating bath and is conveyed, the coating applied to the steel sheet is wiped, and thus, the coating thickness is adjusted and the hot-dip coated steel sheet is manufactured.
In order to manufacture the hot-dip coated steel sheet having uniform coating thickness, it is necessary to make intervals between the wiping nozzle and the front and the rear surfaces of the steel sheet be as constant as possible. Accordingly, in general, a support roll for pressing the steel sheet in a through-thickness direction and flattening the steel sheet shape is installed near an outlet side in the hot-dip coating bath. However, the steel sheet shape cannot be sufficiently corrected by only the support roll, and a warp (a so-called C warp, W warp, or the like) occurs in a transverse direction in the steel sheet which is drawn out to the outside of the hot-dip coating bath.
In the related art, an electromagnetic correction technology, which uses a plurality of electromagnets to correct the warp of the steel sheet, is used. For example, Patent Document 1 discloses that in order to uniformize coating thickness at both ends of a transverse direction of a steel sheet, electromagnetic correction is performed with reference to information of a position in the through-thickness direction of the both ends of the steel sheet which is measured by a separate sensor, and the warp of the both ends of the steel sheet is corrected in an appropriate direction.
Moreover, in Patent Document 2, a technology is disclosed which adjusts dispositions in the transverse direction of a plurality of electromagnets to correspond to a change of a sheet width or meandering of a steel sheet when C warp of the steel sheet is corrected by electromagnets. Moreover, in Patent Document 3, similarly, in order to correspond to the change of the steel width or meandering of the steel sheet, a technology, which moves the electromagnets in the transverse direction, is disclosed.
In addition, in Patent Document 4, a steel sheet shape correction apparatus is disclosed which includes a control unit which automatically adjusts a pass line by moving a pair of support rolls corresponding to the output values of electromagnets on the front side and the rear side of a steel sheet.
Moreover, in Patent Document 5, an apparatus is disclosed in which a plurality of sensors and electromagnets are installed to be opposite to a strip, a position of the strip is detected by a sensor installed in the electromagnet and a sensor installed to be separated from the electromagnet, for example, installed at a position of a wiping nozzle or the like, two signals of the sensors are fed back to currents of the electromagnet, and shape correction of the strip and vibration control of the strip are performed at the position of the wiping nozzle separated from the electromagnet, or the like.
In addition, in Patent Document 6, a continuous hot-dip metal coating method is disclosed in which when a hot-dip metal coating is performed on a metal band by a continuous hot-dip metal coating line which includes a gas wiping nozzle adjusting a coating thickness, a non-contact control apparatus controlling a shape position of a metal band of the gas wiping nozzle portion in a non-contact manner, and a correction roll in a bath correcting the shape of the metal band of the gas wiping nozzle portion in a hot-dip metal coating bath, a determination is performed of whether or not the shape position of the metal band of the gas wiping nozzle portion can be controlled by only the non-contact control apparatus based on at least a thickness of the metal band to be hot-dip metal coated. When the shape position of the metal band of the gas wiping nozzle portion can be controlled by only the non-contact control apparatus, the shape position of the metal band is controlled by only the non-contact control apparatus to make the correction roll in the bath not contact the metal band. When the control of the shape position of the metal band is made difficult by only the non-contact control apparatus, the shape position of the metal band is controlled by only the correction roll in the bath or by using both the correction roll in the bath and the non-contact control apparatus.